RNA tumor virus gene expression will be studied in normal and infected avian cells. Techniques of nucleic acid hybridization and radioimmunoassay will be utilized for the detection and quantitation of specific viral gene sequences and individual viral proteins within the cells. Efforts will be made to evaluate the possible role of specific regulatory mechanisms, and to determine the level at which these controls are exerted. Interactions between exogenous and endogenous viral genes will be studied in order to determine whether regulatory influences are exerted between different viral genomes within the same cell. Particular emphasis will be placed on the study of the virus-related transforming functions, in order to evaluate the relationship between endogenous viral genes and cell transformation, and to elucidate the possible regulatory mechanisms which control the expression of these viral functions.